1. Field of the Invention
The present invention relates to light-emitting diode (LED) drive circuits, light source devices including the LED drive circuits, and display devices including the light source devices.
2. Description of the Related Art
Liquid crystal displays (LCDs) including liquid crystal panels as display devices are widely used. As is generally known, liquid crystal panels display an image by modulating, instead of natural light, white light emitted from so-called “backlight”, which is a light source device, using a video signal.
Cold-cathode tubes are widely employed as light sources for LCDs. Due to improvement in luminous efficiency of LEDs in recent years, LCDs using LEDs as light sources have become known. Compared with cold-cathode tubes, LEDs have the following advantages: LEDs are environment-friendly since they do not use mercury as the material thereof; LEDs can be driven by a lower voltage; LEDs have good temperature characteristics and response characteristics; and LEDs have long life. It is thus expected that LCDs using LEDs will be widely used in the future.
Inventions regarding light source devices (illumination devices) using LEDs as light sources for LCDs, such as those described above, are described in, for example, Japanese Unexamined Patent Application Publication Nos. 2003-100472, 2004-39290, and 2004-319583. These patent documents show the configuration in which a plurality of series-connected circuits including a plurality of LEDs connected in series are connected in parallel with a constant current supply. This configuration further includes a constant-current circuit and a current mirror circuit with respect to the plurality of series-connected circuits, thereby allowing the same level of current to flow through the LEDs and reducing brightness dispersion among the LEDs.